Fire retardant polyvinyl chloride containing compositions

ABSTRACT

Compositions for preparing fire retardant polyvinyl chloride films characterized by their unusual combination of low flame spread, low smoke density, reduced permeability for vapor transmission and good cold crack resistance are described. These film forming compositions comprise a blend of about 40-55% polyvinyl chloride, about 7-20% of chlorinated polyethylene, about 4-20% of a phosphate ester plasticizer, about 3-7% of a magnesium hydroxide filler, about 3-6% of zinc borate and about 3-6% of an antimony trioxide fire retardant with various lubricants, pigments and stabilizers being included where desired. The films derived from the above blend enjoy particular utility in preparing vapor barrier constructions for use in the building trade.

TECHNICAL DESCRIPTION OF THE INVENTION

As is known to those skilled in the art, the construction of buildingsoften requires the use of fire or flame retardant jacketing, facingmaterials for heating duct insulation, and similar applicationsinvolving plies of combustible sheet material or plies of such sheetmaterials laminated to various substrates such as aluminum foil andfiber glass batting. Because of its low cost and versatility, polyvinylchloride (hereinafter referred to as PVC) is often used to prepare suchsheet materials by being blended with various additives which aredesigned to impart the required flame retardant characterisics.

With respect to these fire retardant properties, they may be broken downinto two specific requirements. The first of these involves the abilityof the PVC composition to retard the spread of flame subsequent to beingignited. This factor is referred to as "flame spread". The secondrequirement for fire retardant sheeting relates to the quantity of smokewhich it evolves on burning and is referred to as "smoke density". Thelatter properties are usually evaluated by means of the procedures setforth in Underwriter's Laboratory, Inc. "Standard for Test Method forFire Hazard Classification of Building Materials", subject 723,published August, 1950. Thus, the Underwriter's Laboratory 90B Ratingsrequire a maximum flame spread of 25 and a maximum smoke density of 50for vapor barrier constructions.

Unfortunately, it has not generally heretofore been possible to providefire retardant PVC films and sheeting whose flame spread and smokedensity ratings were both able to meet the minimum standards imposed bythe Underwriter's Laboratory Inc. rating. Thus, where low flame spreadwas achieved, smoke density remained deficient. Conversely, where smokedensity of the PVC film was adequate, its flame spread failed to meetminimum standards. Clearly, therefore, a need is seen to exist for thedevelopment of a PVC composition capable of yielding films which displaya combination of low flame spread and low smoke density.

Thus, it is an object of this invention to provide compositions capableof yielding films and sheeting characterized by their unique combinationof low flame spread and low smoke density. Another object is to form aflame retardant PVC composition having good cold crack properties. Ithas been found that use of chlorinated polyethylene reduces thetemperature at which the film will crack as measured by the MaslandS.P.I. cold crack test. This allows installation of the final product onthe job site at lower temperatures than would ordinarily be possible.Prior art methods of obtaining a lower cold crack point, i.e. throughthe use of adipate plasticizers, adversely affect the flame retardanteffect of the film which results therefrom. Still another object is theformation of excellent vapor barrier compositions. The film formingcomposition also possesses excellent low water transmission propertieswhich is important for the vapor barrier properties of the film. Thiscan be measured by ASTM E96, Method A.

In brief, the products of this invention are film forming compositions,as well as the films and sheets derived therefrom, comprising anintimate admixture of a vinyl chloride polymer, a chlorinatedpolyethylene, a phosphate ester plasticizer, an antimony trioxide flameretardant, a fine particle size magnesium hydroxide filler, and zincborate, together with such ingredients as lubricants, fillers, pigments,and stabilizers, etc., whose presence may be desired by thepractitioner.

The vinyl chloride polymers applicable for use in preparing these novelfilm forming compositions should, preferably, have a low molecularweight which, as expressed in terms of its Relative Viscosity, at 25°C.,as determined in a 1% by weight, solution in cyclohexanone, should be inthe range of from about 2.00 to 2.45, with optimum results beingobtained with vinyl chloride polymers having a Relative Viscosity valueof about 2.20 to 2.30. The use of such low molecular weight vinylchloride polymers in the film forming compositions of this invention isof substantial significance since their presence aids in obtaining thedesired properties of tensile strength, tear strength and goodelongation in the films prepared from these novel compositions.Moreover, the combination of such low molecular weight vinyl chloridepolymers with the high percentage of various inert materials which areutilized in preparing the film forming compositions of this inventionfacilitates the rapid fusion and blending of these compositions.Although PVC is the preferred vinyl chloride polymer for use inpreparing the products of this invention, it should be noted that it isalso possible to employ copolymers of vinyl chloride with minorproportions of one or more ethylenically unsaturated, i.e. vinylcomonomers, including:alpha-olefins, such as ethylene, propylene andbutylene; vinyl esters of carboyxlic acids, such as vinyl acetate, vinylpropionate, vinyl butyrate, and vinyl stearate; the C₁ -C₂₀ alkyl estersof acrylic and methacrylic acid, such as methyl methacrylate, ethylmethacrylate, methyl acrylate, ethyl acrylate, butyl acrylate,2-ethylhexyl acrylate and lauryl acrylate; aryl, halo- and nitro-substituted benzyl esters of acrylic and methacrylic acid such as benzylacrylate and 2-chlorobenzyl acrylate; ethylenically unsaturatedmonocarboxylic-acids, such as acrylic and methacrylic acids;ethylenically unsaturated dicarboxylic acids, their anhydrides and theirC₁ -C₂₀ mono- and dialkyl esters, such as aconitic acid, fumaric acid,maleic acid, itaconic acid, citraconic acid, maleic anhydride, dibutylfumarate and mono-ethyl maleate; amides of ethylenically unsaturatedcarboxylic acids, such as acrylamide and methacrylamide; vinyl arylcompounds, such as styrene and alpha-methyl styrene; nitriles ofethylenically unsaturated carboxylic acids, such as acrylamide andmethacrylamide; vinyl aryl compounds, such as styrene and alpha-methylstyrene; nitriles of ethylenically unsaturated carboxylic acids, such asacrylonitrile and methacrylonitrile; vinyl pyrrolidones, such asN-vinyl-2-pyrrolidone; C₁ -C₂₀ alkyl vinyl ethers, such as methyl vinylether, ethyl vinyl ether and stearyl vinyl ether; dienes, such asisoprene and butadiene; and, glycidyl esters of acrylic and methacrylicacid, such as glycidyl acrylate and glycidyl methacrylate, etc. Thus, itis to be understood that the use in this disclosure of the term "vinylchloride polymer" is meant to encompass both polyvinyl chloride andcopolymers of vinyl chloride with a minor proportion of one or morevinyl comonomers.

The chlorinated polyethylene which also forms a portion of the filmforming composition should have a chlorine content of about 35% to about45%. Suitable chlorinated polyethylenes are Dow Chemical Co's CPEblending or compounding resins.

The phosphate ester plasticizers applicable for use in the PVC filmforming compositions of this invention are orthophosphate esters such astriaryl phosphates, e.g., tricresyl phosphate, cresyl diphenylphosphate, isopropylphenyl diphenyl phosphate, alkyl diaryl phosphates,e.g., diphenyl 2-ethylhexyl phosphate; aryl dialkyl phosphate andmixtures thereof and trialkyl phosphates, e.g., tris(dichloropropylphosphate; orthophosphate ester plasticizers resulting from thephosphorylation of naturally occurring materials such as coal tar asdescribed in British Pat. No. 837,679; as well as syntheticallymanufactured ortho-phosphate ester plasticizers as described in BritishPat. No. 1,146,173. These plasticizers are relatively involatile andprovide the resulting films with good low temperature flexibilitycharacteristics.

The antimony trioxide flame retardant which is incorporated into thefilm forming compositions of this invention should, preferably, have aparticle size below about 5 microns and a fineness such that about97.2%, by weight, will pass through a 325 mesh U.S. Standard Screensize. Its presence serves to substantially reduce the smoke density andalso contributes to the reduction of flame spread in the PVC filmsderived from these film forming compositions. Particularly useful forthis purpose is a composition containing:

a. a major proportion of a mixture of the cubic, i.e. senarmonite, andorthorhombid, i.e. valentinite, crystallographic forms of antimonytrioxide with (b) a minor proportion of magnesium and sodium compounds.A commercially available material conforming to the latterspecifications is the product sold under the trademark "Thermoguard B"by M & T Chemicals, Inc.

Another required component of the unique film forming compositions ofthis invention is a fine particle size, magnesium hydroxide filler withthe use of the naturally occurring mineral brucite being preferred. Thelatter should preferably have a particle size such that at least 99% ofthe particles have a diameter of less than 45 microns. In addition, itshould have a low oil absorption value, preferably in the range of about22 cc/100 grams. This filler serves to further enhance the flame spreadand smoke density characteristics of the films derived from the PVC filmforming compositions of this invention. Being naturally derivedproducts, these magnesium hydroxide fillers will often contain traceamounts of other elements such, for example, as calcium, copper, ironand silicon. Exemplary of the magnesium hydroxide fillers applicable foruse in these novel compositions is the product sold under the trademark"S/G 84" by the Burns & Russell Company which comprises brucite withsome MgCO₃ and/or Mg(OH).sub. 2 -- 2MgSO₄ being present as minorcomponents.

The film forming composition of the present invention also contains zincborate. This salt has been found to substantially reduce the flamespread and smoke density of the film forming composition.

With respect to proportions, the film forming composition of thisinvention should contain from about 40 to 55%, by weight, of a vinylchloride polymer, from about 7-20% of the chlorinated polyethylene, fromabout 4 to 20%, by weight, of the selected phosphate plasticizer, fromabout 3 to 6%, by weight, of the antimony trioxide flame retardant, fromabout 3 to 7%, by weight, of the fine particle size magnesium hydroxidefiller, and from about 3-6%, by weight, of zinc borate.

It is to be understood that all of the above stated proportions arebased upon the total weight of the resulting film forming composition.

As has been noted, hereinabove, the film forming compositions of thisinvention may, if desired, be prepared so as to contain effectiveamounts of various optional ingredients. Thus, one may introduce fillersand pigments such, for example, as talc, calcium carbonate, mica andclay; lubricants such, for example, as stearic acid, calcium stearate,polyethylene and various waxes; and, stabilizers such, for example, asoctyl epoxy tallate, epoxidized soya bean oil, barium-cadmium-zinccomplex salts, organic phosphates, tin containing compounds, and leadcontaining compounds. If a non-blocking film is desired, about 0.1 toabout 0.5%, by weight, of a lubricant such as stearic acid or calciumstearate and from about 0.1% to 0.5% of a partially oxidizedpolyethylene such as Allied Chemical Co.'s 629A, should be present inthe formulation.

The actual preparation of the film forming compositions of thisinvention will ordinarily involve the initial step of admixing of thesolid ingredients including the PVC, the antimony trioxide flameretardant, the zinc borate, the magnesium hydroxide filler and anyoptional pigments and other solid materials in a blender. Anyconventional blender apparatus, such for example, as a ribbon blenderand high speed mixers such as the Henschel mixers can be utilized forthis purpose. The required phosphate plasticizer, as well as any desiredoptional ingredients which are liquids, are then blended with oneanother and are thereupon added to the solid PVC containing mixture. Thechlorinated polyethylene is added and all ingredients are mixed over aperiod of about 30 minutes. At this point, any lubricants whose presenceis desired should be blended with the composition over a period of about10 minutes.

Next, the now complete composition should be treated in an apparatuscapable of fluxing it and thereby producing an exceedingly uniformcomposition. Suitable equipment for this purpose includes the Intermixsold by Adamson United and the Kokneader sold by Baker Perkins. It isimportant that this operation should also serve to drive off as manyvolatile components from the composition as is possible. Thus, thepresence of an excessive concentration of volatiles will have adeleterious effect upon the flame spread and smoke densitycharacteristics of the films derived from these compositions. Moreparticularly, it is preferred that the concentration of volatiles inthese film forming compositions should be no more than about 2.0%, byweight, when tested for three hours in a circulating air oven at 220°F.Subsequent to the fluxing operation, the resulting composition may thenbe stored or immediately passed through a calender or other suitableapparatus which is capable of sheeting it into the form of a thin,self-supporting film. The resulting films may have a thickness in therange of from about 2 to 60 mils with a thickness of about 3.2 milsbeing optimum for most purposes. Those skilled in the art will, ofcourse, realize that the above described preparatory procedure is merelyillustrative and may be varied, as desired, in any convenient manner.

The films derived from the novel film forming composition of thisinvention display flame spread and smoke density characteristics wellbelow those heretofore attainable. They are therefore, exceptionallywell suited for use in any number of building construction applicationswherein the materials utilized must display flame retardant properties.Thus, these films can be used for the preparation of vapor barrierconstructions by being laminated to a section of fiber glass battinghaving a thickness of about 0.25 to 3.0 inches with a suitable fireretardant adhesive such as, for example, the aqueous based adhesivescontaining one or more vinyl type homo- or copolymers dissolved oremulsified therein.

The following examples will further illustrate the embodiment of thisinvention. In these examples all parts given are by weight unlessotherwise noted.

Example I

This example illustrates the preparation of a preferred PVC film formingcomposition typical of the novel products of this invention as well asits subsequent conversion into the form of a self-supporting film.

A total of 41.554 parts of a low molecular weight PVC resin having aRelative Viscosity as determined in a 1%, by weight, solution incyclohexanone, at 25°C., of 2.25 was mixed, at ambient temperature, in aribbon blender together with 4.87 parts of an antimony trioxide flameretardant ("Thermoguard B"), 4.27 parts of zinc borate flame retardantand 4.3 parts of a magnesium hydroxide, (brucite), filler ("S/G 84").Next, 14.5 parts of diphenyl 2-ethylhexyl phosphate, 3.5 parts of octylepoxy tallate, 3.0 parts (in equal portions) of two barium-cadmiumcontaining stabilizers, sold by the Nuodex Division of TennecoChemicals, Inc. as "Nuostabe V-1541" and "Nuostabe V-1542", were blendedtogether and then combined with the PVC containing mixture. About 15.18parts of chlorinated polyethylene (Dow Chemical CPE) was then added, andthe resulting product was intimately admixed for 30 minutes. To theresulting blend, there was then added, as a lubricant, 0.2 parts ofstearic acid and 0.2 parts of calcium stearate. The now completecomposition was admixed for an additional 10 minutes then conveyed to aKokneader apparatus where it was thoroughly fluxed over a period of 1 to2 minutes thereby providing it with a high degree of uniformity. Thecomposition was then calendered so as to yield a film having a thicknessof about 3.2 mils.

When a sample of this film was evaluated by means of the proceduredescribed in Underwriter's Laboratory, Inc. "Standard for Test Methodfor Fire Hazard Classification of Building Materials, Subject 723 (UL 90B ratings)" it was found to have excellent fire retardant properties asshown by its flame spread value of 17.9 and its smoke density value of78.1. The cold crack resistance was rated "pass" at -20°F. (MaslandS.P.I. cold crack test, ASTM D1790-62) and the water vapor transmissionwas 0.86 g/100 in² in 24 hours (ASTM E-96, Method A).

This film was then used for the preparation of a vapor barrierconstruction by being laminated to a 1 inchthick section of a fiberglass batting using an aqueous based adhesive composition having a vinylchloride polymer dissolved therein. The resulting product was tested andwas found to have a flame spread value of 20 and a smoke density valueof 45.

EXAMPLE II

A series of film forming compositions according to the present inventionwere formulated according to the above procedure. Table 1 set forthbelow gives their composition and flame, smoke and water generationcharacteristics when tested as a film.

                                      TABLE 1                                     __________________________________________________________________________                      FILM                                                                          1     2     3    4     5    6                               Polyvinyl Chloride Homopolymer                                                                  53.355                                                                              43.554                                                                              42.01                                                                              43.554                                                                              47.08                                                                              42.73                           Chlorinated Polyethylene.sup.1                                                                  --    12.185                                                                              9.40 10.176                                                                              9.40 15.176                          Phosphate Plasticizer                                                         Diphenyl 2-ethylhexyl phosphate.sup.2                                                           --    --    --   14.185                                                                              --   --                              Decyl diphenyl phosphate.sup.3a                                                                 17.13 --    --   --    5.38 14.533                          Tris(dichloropropyl) phosphate.sup.3                                                            --    6.092 --   --    --   --                              Cresyl diphenyl phosphate                                                                       --    --    8.38 --    --   --                              Epoxy tallate plasticizer                                                                       5.81  5.81  3.81 3.81  1.87 3.000                           Antimony trioxide.sup.4                                                                         4.87  4.87  5.64 4.87  5.64 4.87                            Magnesium hydroxide.sup.5                                                                       4.30  4.30  4.70 4.30  4.70 4.30                            Zinc borate       4.27  4.27  4.70 4.27  4.70 4.27                            Stearic acid      0.20  0.20  0.10 0.20  --   0.20                            Calcium stearate  0.20  0.20  0.10 0.20  --   0.20                            Hydrated alumina  --    --    9.39 --    9.39 --                              Trimethanol propane triheptanoate                                                               --    6.092 --   --    --   --                              Titanium dioxide  7.785 7.785 7.76 7.785 6.70 7.785                           Barium Cadmium soap.sup. 6                                                                      1.04  1.04  1.50 1.5   0.52 1.418                           Barium Cadmium Zinc liquid.sup.7                                                                1.04  1.04  1.50 1.5   2.75 1.418                           Partially oxidized polyethylene.sup.8                                                           --    0.20  --   0.20  --   0.100                           Hexyldecyl Adipate                                                                              --    --    2.00 --    1.87 --                              Product Characteristics                                                       Flame Spread.sup.9                                                                              15.38 15.38 15.38                                                                              12.85 12.82                                                                              15.5                            Smoke Generation.sup.10                                                                         105.0 94.00 75.30                                                                              88.40 34.5 58.8                            Cold Crack Resistance.sup.12                                                                    Pass  Pass  Pass Pass  Pass Pass                                              0°F.                                                                         -10°F.                                                                       0°F.                                                                        -10°F.                                                                       +10°F.                                                                      -20°F.                   Water Vapor Transmission.sup.11                                                                 1.32  --    --   --    0.23 1.17                            __________________________________________________________________________     All values for the various ingredients given above are % by weight, based     on the weight of the entire formulation.                                      .sup.1 Contains about 35%- 45% chlorine. Suitable chlorinated                 polyethylenes are available from Dow Chemical Co.                             .sup.2 Santicizer 141, sold by Monsanto.                                      .sup.3 Fyrol FR-2, sold by Stauffer Chemical Company.                         .sup.3a Santicizer 148, sold by Monsanto.                                     .sup.4 Thermoguard B, sold by M & T Chemicals Co.                             .sup.5 S/G 84, sold by Burns & Russell Co.                                    .sup.6 Nuostabe V-1541 Stabilizer, sold by Tenneco Chemicals Co. or Mark      WSX, sold by Lankro Chemicals Ltd.                                            .sup.7 Nuostab V-1542 Stabilizer, sold by Tenneco Chemical Co., or Mark       739, sold by Lankro Chemicals Ltd.                                            .sup.8 Allied Chemical Co. 629 A                                              .sup.9 Flame spread and smoke generation are measured by the Underwriter'     .sup.10 Laboratory "Standard Test for Fire Hazard Classification of           Building Materials", subject 723, published 1950. The UL 90 B ratings         require a flame spread of no more than 25 and a maximum smoke density of      about 50 for flame barrier constructions.                                     .sup.11 Measured according to ASTM test method E 96, Method A, and given      in grams/100 in.sup.2 in 24 hrs.                                              .sup.12 Masland S.P.I. cold crack test, ASTM D1790-62.                   

What is claimed is:
 1. A vapor barrier construction comprising aself-supporting film which is adhesively laminated to a fiberglassbatting, said self-supporting film comprising an intimate admixture of:(1) a vinyl chloride polymer; (2) a chlorinated polyethylene having achlorine content of from about 35% to about 45%; (3) a phosphate esterplasticizer; (4) an antimony trioxide flame retardant having a particlesize of below about 5 microns; (5) a magnesium hydroxide filler having aparticle size such that at least 99% of the particles have a diameter ofless than 45 microns; and, (6) zinc borate.
 2. The vapor barrierconstruction of claim 1, wherein said vinyl chloride polymer has aRelative Viscosity, as determined with a 1%, by weight, solution incyclohexanone, at 25°C., in the range of from about 2.00 to 2.45.
 3. Thevapor barrier construction of claim 2, wherein said vinyl chloridepolymer has a Relative Viscosity of about 2.20-2.30.
 4. The vaporbarrier construction of claim 1, wherein said vinyl chloride polymer ispolyvinyl chloride.
 5. The vapor barrier construction of claim 1,wherein said phosphate plasticizer in said film is diphenyl 2-ethylhexylphosphate.
 6. The vapor barrier construction of claim 1, wherein saidantimony trioxide fire retardant in said film comprises a compositioncontaining a major proportion of a mixture of the cubic and orthorhombicforms of antimony trioxide.
 7. The vapor barrier construction of claim1, wherein said magnesium hydroxide filler in said film comprisesbrucite having a particle size such that 99% of its particles have adiameter of less than 45 microns and an oil absorption value of about 22cc/100 grams.
 8. The vapor barrier construction of claim 1, wherein saidfilm contains from about 40 to 55% of a vinyl chloride polymer; fromabout 7-20% of said phosphate ester plasticizer; from about 3 to 6% ofsaid antimony trioxide flame retardant; from about 3 to 7% of saidmagnesium hydroxide filler; and about 3-6% of zinc borate; all of thelatter proportions being based on the total weight of said film.